At least for Flink a solution could be to set the parallelism of the "WriteBundles" ParDo to the number of shards. Then the behavior would be correct. Problem is just that the Flink runner (or any runner) doesn't know about the special nature of these three ParDo functions.
On Tue, 7 Jun 2016 at 01:16 Robert Bradshaw <[email protected]> wrote: > A preferable solution would be to augment the Beam sinks to support > these parameters. At the very least, we should probably make running > these with fixed shards a loud error in the meantime. > > On Wed, Jun 1, 2016 at 4:17 AM, Aljoscha Krettek <[email protected]> > wrote: > > Hi, > > the issue is a bit more complicated and involves the Beam sink API and > the > > Flink runner. > > > > I'll have to get a bit into how Beam sinks work. The base class for > sinks is > > Sink (TextIO.write gets translated to Write.to(new TextSink())). Write.to > > normally gets translated to three ParDo operations that cooperate to do > the > > writing: > > > > - "Initialize": this does initial initialization of the Sink, this is > run > > only once, per sink, non-parallel. > > > > - "WriteBundles": this gets an initialized sink on a side-input and the > > values to write on the main input. This runs in parallel, so for Flink, > if > > you set parallelism=6 you'll get 6 parallel instances of this operation > at > > runtime. This operation forwards information about where it writes to > > downstream. This does not write to the final file location but an > > intermediate staging location. > > > > - "Finalize": This gets the initialized sink on the main-input and and > the > > information about written files from "WriteBundles" as a side-input. This > > also only runs once, non-parallel. Here we're writing the intermediate > files > > to a final location based on the sharding template. > > > > The problem is that Write.to() and TextSink, as well as all other sinks, > are > > not aware of the number of shards. If you set "withoutSharding()" this > will > > set the shard template to "" (empty string) and the number of shards to > 1. > > "WriteBundles", however is not aware of this and will write 6 > intermediate > > files if you set parallelism=6. In "Finalize" we will copy an > intermediate > > file to the same final location 6 times based on the sharding template. > The > > end result is that you only get one of the six result shards. > > > > The reason why this does only occur in the Flink runner is that all other > > runners have special overrides for TextIO.Write and AvroIO.Write that > kick > > in if sharding control is required. So, for the time being this is a > Flink > > runner bug and we might have to introduce special overrides as well until > > this is solved in the general case. > > > > Cheers, > > Aljoscha > > > > On Wed, 1 Jun 2016 at 07:37 Jean-Baptiste Onofré <[email protected]> > wrote: > >> > >> Yes, just tested, it happens only with the flink runner. > >> > >> Agree to create a Jira. > >> > >> Regards > >> JB > >> > >> On 06/01/2016 03:41 AM, Davor Bonaci wrote: > >> > This will be a runner-specific issue. It would be the best to file a > >> > JIRA issue for this. > >> > > >> > On Tue, May 31, 2016 at 9:46 AM, Jean-Baptiste Onofré < > [email protected] > >> > <mailto:[email protected]>> wrote: > >> > > >> > Hi Pawel, > >> > > >> > does it happen only with the Flink runner ? I bet it happens with > >> > any runner. > >> > > >> > Let me take a look. > >> > > >> > Regards > >> > JB > >> > > >> > On 05/30/2016 01:38 AM, Pawel Szczur wrote: > >> > > >> > Hi, > >> > > >> > I'm running a pipeline with Flink backend, Beam bleeding edge, > >> > Oracle > >> > Java 1.8, maven 3.3.3, linux64. > >> > > >> > The pipeline is run with --parallelism=6. > >> > > >> > Adding .withoutSharding()causes a TextIO sink to write only > one > >> > of the > >> > shards. > >> > > >> > Example use: > >> > > >> > > data.apply(TextIO.Write.named("write-debug-csv").to("/tmp/some-stats")); > >> > vs. > >> > > >> > > data.apply(TextIO.Write.named("write-debug-csv").to("/tmp/some-stats")*.withoutSharding()*); > >> > > >> > Result: > >> > Only part of data is written to file. After comparing to > sharded > >> > output, > >> > it seems to be just one of shard files. > >> > > >> > Cheers, > >> > Pawel > >> > > >> > > >> > -- > >> > Jean-Baptiste Onofré > >> > [email protected] <mailto:[email protected]> > >> > http://blog.nanthrax.net > >> > Talend - http://www.talend.com > >> > > >> > > >> > >> -- > >> Jean-Baptiste Onofré > >> [email protected] > >> http://blog.nanthrax.net > >> Talend - http://www.talend.com >
